by Arnie Schoenberg
Figure 7.1 Linnaeus' description of Homo monstrosus. Linné, Carl von. Systema naturae [...] Editio decima tertia [Lyon]. Tomus primus [pars I]; [Regnum animale], 1789 Real Jardín Botánico (public domain)
7 human variation
7.1.1 evo devo
7.1.3 human life cycles
184.108.40.206.1 secular trend
220.127.116.11 grandmother hypothesis
7.2.2 altitude sickness
7.2.3 the epidemiological transition
18.104.22.168 lifestyle diseases
22.214.171.124 the evolution of infectious disease
7.2.4 lactose intolerance
7.3.1 biocultural glossary
7.4.1 Bergman's rule
7.4.2 Allen's rule
The previous paleontology and paleoanthropology sections tried to answer the question: How are humans different from other life? This section on human variation asks the question: How are humans different from each other?
Go back and review the Mendelian traits lab. Should we take everyone in class with attached earlobes and call them a race? This sounds silly, but what I hope you can appreciate is that from a biologist's perspective, assigning a race to people based on an arbitrary range of skin colors and facial features is even sillier. Anthropologists have a kind of dissociative identity disorder when it comes to race. When you ask people about human variation, the first thing that usually comes to mind is race – they acknowledge the concept. So race exists, and cultural anthropologists study it as a learned behavior. Physical anthropologists split between denying the existence of race, and seeing it empirically in bones. Forensic anthropologists still like to talk about being able to "race a bone", which means establish the ancestry of an individual from the morphology of skeletal remains. Since the early 1900s, most anthropologists in all subfields have actively opposed racism.
More biologically significant kinds of human variations include our practically invisible co-evolution with disease, and solving important riddles such as 1) If men are from Mars, and women from Venus, does that make Earthlings intersexual? and 2) What walks on four legs in the morning, two legs in the afternoon, and three legs in the evening?
Humans have the longest life span of any primate. Orangutans live to be about 60 but we average another third of a life on top of that. We are the longest living out of any mammal and most life on the planet. It makes us ask why natural selection selected so many old people.
Figure 7.2 average life spans of primates by Script & Seal © 2010
Epigenetics refers to changes beyond the four forces of evolution. Your chromosomes can change during your lifetime. The term genetic mosaic refers to a group of cells in the body with variation in their DNA. Don't confuse mosaic evolution with genetic mosaicism.
* DNA responds to signals from outside the cell.
* article on Genetic Mosaic in the Brain
* article on Mother's diet can lead to alterations in her child's DNA
Evo Devo went beyond the Modern Synthesis and focused evolutionary theory on the development of the embryo (Stanford 2012).
People who don't understand evolution often struggle with trying to explain why human fetuses have things that look like tails and gills.
Figure 7.3 Vertebrates (bat, gibbon, human) at three stages of development by Ernst Haeckel Das Menschen-Problem und die Herrentiere von Linné. 1907. (Public Domain)
Figure 7.4 Human embryo, 7th week of pregnancy by Ed Uthman (CC BY 2.0)
But if you understand our ancestry it makes perfect sense
that our DNA is just a bunch of variations away from fish DNA. There is a
grandiloquent phrase to describe this phenomenon, which you can use to impress
people at cocktail parties: "Ontogeny recapitulates phylogeny."
Ontogeny is the development of the individual through various life stages. To
recapitulate is to briefly summarize. Phylogeny is the evolution of a species, that we studied in the paleontology section. So,
this idea is that the development of the individual is a brief summary of the
development of the species. The idea goes way back to Lamarck's time, and has
been abused and misused for a long time, and you should not think of it as a
scientific law that applies to all cases, and be very wary of people who talk
about our "reptilian brain", for example, because our brain is not
just a fish brain, enclosed by a reptile brain, enclosed by a human brain, and
that kind of simplification can be very misleading. But, I think the idea is
useful as a metaphor, something not true, but just a good reminder that we
share relatives with fish, and that evolution tends to build on structures that
are already there.
(see: Gould, Stephen Jay. 1977. Ontogeny and Phylogeny. Cambridge Mass.: Belknap Press of Harvard University Press.)
Figure 7.5 Your earliest baby portraits, * Ontogeny, by Zephyris (CC BY-SA 3.0 or GFDL)
We can apply evolutionary theory, cellular biology, primatology, genetics, and most of the other subfields we've studied so far to better understand how humans change over our lifetimes.
During childhood body growth slows slightly until adolescence, but brain growth peaks around age 5.
* article on peak glucose use in childhood brains
hypotheses for risk taking; insurance companies
[make mouse trap graphic]
research on Bonobo thyroid hormones and life stages vocabulary: ontogenetic
The average age of menarche has continued to fall since the 1800s, and as good anthropologists we should beware of unicausal arguments and consider all the possible contributing factors, like improved diet and health, and environmental contaminations such as hormones (from discarded birth control pills and animal products) and similar chemicals found in plastics.
One factor in both aging and epigenetic change are the ends of your chromosomes, your telomeres which tend to wear out when they get bumped around.
Figure 7.6 * Huzen, J., van Veldhuisen, D.J., van Gilst, W.H. and van der Harst, P. (2008), Telomeres and biological ageing in cardiovascular disease, Ned. Tijdschr. Geneeskd., vol. 152, pp. 1265–1270, with permission from the Nederlands Tijdschrift voor Geneeskunde.
Most animals reproduce until they die. Natural selection selects against a"wasted" life. So why do humans live so long? Why do women tend to live so long after they stop reproducing?
* testing the grandmother hypothesis in Utah
* with killer whales
A disease is just what it says: a "dis" - "ease"; meaning something is keeping you from being at ease, or your normal state. From a system theory approach, disease is a stressor that moves the body out of homeostasis. There are many kinds of diseases that are important to human evolutions. We've already discussed genetic diseases in section 2, but here we are going to look at human variation as a response to infectious disease.
With infectious diseases, the concept of coevolution is important to understand. While humans are evolving, our diseases are also evolving (and unfortunately, usually faster than we do).
The study of diseases on a large scaled is called epidemiology.
Looking at the history of humanity most of our genetic diseases were dealt with through natural selection. For most of history the most important disease we suffered from was malnutrition. People were more worried about starving to death than anything else. If a small band of hunter-gatherers got a bad infectious disease, they just all died, and took the disease with them. As population density increases, we are exposed to more diseases.
Most of the selection for disease resistance is at the molecular level. * Watch this example of evolution of immunity:
* balanced polymorphisms in humans
Paleopathology is the study of the effects of disease on human remains from archaeological sites.
* "Black death skeletons reveal pitiful life of 14th-century Londoners"
Anything that takes us out of our biological comfort zone can cause natural selection. High altitude is associated with several stressors including less available oxygen, cold, and resource scarcity. Highlanders tend to be different than lowlanders, both genetically and culturally.
* read Wikipedia's description of altitude sickness
* genes found in Tibetans that help them survive high altitude shared with Denisovans
We can see human history as changes in the prevalence from one class of diseases to another:
As hunter-gatherers the main thing that killed us was starvation. If a typical isolated band of 25-50 people caught a nasty disease, the entire band would die, and the disease would die with it.
When we started agriculture, we increased population density, became sedentary, and basically started living in our own shit, not to mention that of all our domesticated animals. Agriculture was a big trade off: we had more food and didn't starve as much, but we had to deal with more infectious diseases. Most archaeological research shows that when agriculture was introduced the population went up, but the health and life expectancy of the individual went down.
Worst Mistake In The History Of The Human Race"
by Jared Diamond, Prof. UCLA School of Medicine
Discover-May 1987, pp. 64-66
The "zoo" in zoonosis and zoonotic just means "from animals", and the origin of many human diseases came from other animals. A vector in epidemiology refers to something that transfers the disease to the human. Considering what we learned about the taxonomy of mammals, it makes sense that we catch more diseases from chimpanzees than we do from opossums. The closer we are taxonomically on our family tree, the closer our genetic makeup, the more similar the proteins, the more similar the body provides an environment and ecological niche, and thus the more likely it is for pathogens to jump from one species to another.
Another contributing factor is that for most domesticated animals, domestication was made easier because our similar taxonomy determined that we shared similar social structures and communication systems, so it was easier to domesticate animals that were more like us.
Figure 7.7 disease vectors (permission pending)
One reason bats have been an important vector in diseases like Ebola is because they can fly long distances and spread the pathogens to a wide geographic area. The other reason has to do with understanding our taxonomy, our place in the animal kingdom. As mammals, bats are so similar to us that they provide almost identical environments for the pathogens to live, evolve, and then easily cross over to humans, with only small modifications necessary. This is same reason why it's especially bad for humans to eat primates.
Mosquitos don't get the same diseases as we do, they function as disease vectors, like a shared needle, in passing blood and pathogens from one person to another.
* Mosquitos decide who to bite based on your genetics
Figure 7.8 Female Aedes aegypti mosquito used in the experiment to test attractiveness to odors from the hands of identical and non-identical twins. by G. Mandela Fernández-Grandon, et al. * "Heritability of Attractiveness to Mosquitoes" PLOS (CC BY)
We didn't evolve to sit motionless at a computer screen for hours a day. Millions of years of evolution set us up to be climbing or running around gathering and hunting for food. And for most of that time there wasn't enough food to go around. When food is too fast and too cheap, we get fat. Quick calories were once rare and expensive. Most hunter-gatherers were getting most of their calories from fruits, leaves, tubers, and nuts. Meat was scarce, and the rest hadn't been invented yet. When medicine and abundant food kept us fed and free of infectious disease, we started dying from type II diabetes and heart disease.
The idea of a "paleo diet" acknowledges our long history as foragers and tries to recreate a pre-agriculture diet.
Figure 7.8 peanut bar wrapper from UMCHU, photo by Arnie Schoenberg © 2014
This bar was really tasty (yum!), and healthier than a Snickers Bar, but none of the ingredients (neither the peanuts, the rice syrup, nor the salt) were a regular part of our ancestors' diet. I think trying to justify your diet using your evolutionary past might be a good metaphor for health, but the scientific support is not conclusive. Primate and hominid diets varied depending on the time and place. We now live in an urban, sedentary, environment and shouldn't expect our ideal diet to be the same as some idealized past. We can survive on an astonishing variety of foods, both too little and too much.
* Too tired to chew; meat and evolution
* documentary about "Our Hunter-Gatherer Past: Episode 2 of Food, Science, and the Human Body" (available on Netflix or Kanopy):
* article on Paleo diet
* graph of relative cost of food worldwide
Remember that when we take antibiotics, we don't kill everything, and when the new population multiplies, natural selections means that they tend to have the variations that make them resistant to the antibiotics. You might expect this evolution to be slow because the variation from sexual reproduction (meiosis) is mostly absent, but you have to take into account the length of time of each generation. Human evolution is slow because it takes about 20 years from when you're born to when you reproduce, whereas baby E. coli bacteria are fissioning (mitosis) about 20 minutes after their born. Go back and watch the video of bacteria evolving resistance in the Mutation section.
Figure 7.9 * "National Goals for Reducing Inappropriate Antibiotic Use in Outpatient Settings" 2016 Pew Charitable Trust, Antibiotic Resistance Project (permission pending)* listen to a 2017 PEW podcast: "Antibiotic Resistance: When Drugs Don't Work Anymore"
* 2014 World Health Organization report on antimicrobial resistance
* New Type of Antibiotic Resistance Raises Alarm
* Understanding sex, drugs, and HIV
* SARS Corona virus
But not all pathogens are evolving faster that our culture can keep up with. Many viruses are slow to change, and we can get ahead of them if we all work together.
Should you vaccinate your child?
YES! Vaccines do NOT cause autism. Join humanity's struggle against infectious disease. It is amazing to think that humans have actually driven a few viruses into extinction. Let's pat ourselves on the back!
Vaccines have an exponential effect because of a phenomenon known as "herd immunity". When the percentage of immunized people reaches a critical level, there is hardly anyone around to spread the disease to.
Figure 7.10 * Herd Immunity by Tkarcher (CC BY-SA 4.0)
* Vaccines and Autism: A Tale of Shifting Hypotheses
People have a right to get mad at you for not getting your shots or taking antibiotics when you don't need them. Your ignorance could make them sick.
Even though pathogens continue to evolve, medicine seems to be getting better because our cultural progress continues at a fast pace too. One area of growth is applying our understanding of genetics to medicine and develop individualized treatments based on a patient's genome.
* pharmagenomics and personalized medicine
* Obama's initiative for Precision Medicine
Look back at our discussion of lactase persistence as a Mendelian trait. Lactase persistence means you keep producing lactase as an adult; lactose intolerance is the opposite, you can't digest milk. In this section we are examining the same trait, except that we are trying to explain how natural selection may have caused it. What are the selective advantages and disadvantages to being able to digest milk as an adult? How does culture effect our biology? It's amazing to think of Nigeria the different rates of lactose tolerance of different people within the same country.
Dennis O'Neil on Nutritional Adaptation
* article on the genetics of smell
* article on European Lactose Intolerance
We're experiencing a third epidemiological transition: a return of infectious diseases
COVID-19 brought zoonotic diseases to the front-burner, and even my little niece was telling me all about bats and pangolins. Protecting wildlife, protect yourself; you can save two birds with one phone.
Figure 7.11 Intersex butterflies circa 2014 (permission pending)
The difference between sex and gender is a great example of biocultural synthesis, but the terms can get confusing, so I've included a glossary below. Although language changes and there are gray areas, it's better to get the commonly used definition down first, and then go into to the controversies.
1) Sex in biological anthropology refers to whether when you peek inside the nucleus of each of your cells at the 23rd pair of chromosomes you see a stumpy Y chromosome or a second X chromosome (XX or XY). The 23rd chromosome codes mostly for genitals and secondary sexual characteristics like robusticity, pelvic shape, hair patterns, mammary gland function, fat distribution, and a bunch of others we're still figuring out, including maybe the structure of the brain. You can ask a forensic anthropologist what their plans for the weekend are, and with straight face, they might say, "I'm going to sex that bone on the table." We often use the terms male and female to refer to sex.
read Hector Reynoso's Sexual Body Size Dimorphism
2) Things get confusing because cultural anthropology often borrows the other popular definition of sex, which should probably be more specifically referred to as love, affection, eroticism, coitus, genital rubbing, mounting, penetration, fertilization, insemination, or whatever is specifically being described, but our Puritan heritage tends to get in the way, and we usually blush and use a general euphemism to avoid embarrassment.
Humans tend to take biological phenomena and shroud them in all kinds of very complicated cultural trappings. Gender refers to the cultural patterns associated with sex. The fact that girls wear pink and boys wear blue is not genetically hardwired on our 23rd chromosomes, it's a cultural rule that we are taught from the first moment we're born and wrapped in a blanket that codes our respective gender, and we're taught the scripts that go along with that gender. We often use the terms man and woman to refer to gender. There is a statistical tendency for most males to be men (XY & wears blue), and most females to be women (XX & wears pink), but this is not a rule; there are also male women (XY & wears pink), and female men (XX & wears blue), and all kinds of variations between those extreme examples.
How you think of yourself.
How you express yourself to other people.
Humans like to think in twos; perhaps because 2 almost the first whole number you get to when counting, perhaps because of our bilateral symmetry that we share with all vertebrates, perhaps because of dualistic cosmologies popular around the world, such as Manichaeism. Because of the duality inherent in meiosis, your sex is mostly determined by whether your father contributed an X or a Y 23rd chromosome.
a continuum, the opposite of binary. Polygenic traits are expressed as clines, like the way a meteorologist doesn't just tell you it's cold here and it's hot there, but they show a map with concentric smooth polygons with temperatures. Even though your biological sex is mostly binary, it is also on a continuum.
"Sexual" refers to male or female. "di" means two. "morph" means shape. The term refers to the biological differences between males and females of the same species.
"Sexual" refers to eroticism. Whom your body feels attracted to.
"Sexual" refers to eroticism. Whom you prefer to be erotic with. "Orientation" implies more biological determinism than "preference", and since most people don't have conscious control over whom they're attracted to, "orientation" is usually more accurate.
"Sexual" refers to eroticism and male or female. This is Charles Darwin's term for the kind of natural selection that was more about reproduction (which implies fertilization)
"Homo" means same, like our genus name, which refers to how these hominids are the same as us. The "sexual" part is very ambiguous and includes both definitions of sex mentioned above and often gender. A more accurate term might be "homosex(gender)sexuality" but please don't start using it. "Hetero" means different. "Bi" means both. This term is being phased out because of its use in portraying sexuality as mental illness.
a man or male who is erotic with men or males, can be broadened to someone who is erotic with the same sex/gender (also, someone who is happy)
a woman or female who is erotic with women or females (also, someone from the Greek island of Lesbos)
transgenderA general term for males who adopt women's culture, and females who adopt men's culture.
Men or males who wear women's clothes; women or females who wear men's clothes, without any implications of eroticism. Crossdressers are often heterosexual.
"Trans" means across, "vest" means clothing. An older term with the same word roots as crossdresser but has more of an erotic connotation.
"Sexual" here refers to male or female. Someone who is in the wrong body and may take hormone supplements and have sexual reassignment surgery to change sexual characteristics of their body. The term is being phased out because it sounds too clinical. "Cissexual" is the opposite, people who feel they were born in the right body.
a catch-all term for gender variation
"Sex" here refers to male or female, "inter" means in between. Non-disjunction of the 23rd chromosome, crossing over of the SRY gene, genes that interfere with sex determining hormones, and other factors can effect the genetic coding and expression of genitals and secondary sexual characteristics, so that many individuals are born not fitting neatly into the extreme biological stereotypes of male and female. The old term for this was "hermaphrodite" (from a Greek myth about the child of Hermes and Aphrodite).
a once derogatory term that has been reclaimed as a catch-all for variations of the terms above. (also, someone who is strange)
"fear of [...] "
You might expect something like sex and eroticism to be wrapped-up with fear and anxiety. Many anthropologists such as Margaret Mead have argued that the fear of sex is culturally determined and is not universally present in all societies and we can find many variations of sexual and gender roles, such as the Twin Spirits, Hijra, Etoro and Sambia warriors, etc. This suggests that our own culture's transphobias, homophobias, and genderphobias are not biologically determined, and can be easily changed through education and political action.
The glossary was adapted from the National Center for Transgender Equality and Gay Alliance
It's important to remember that most of these terms are adjectives that make small qualifications to the main identity of the subject; most of these terms should be followed by the most important word, "person", and we need to remember how small (if any) a genetic variation we are talking about; we may make a big deal about this part of someone's social identity, but on the genetic level it represents an insignificant difference between people.
* 5 part video series by Desmond Morris “The Human Sexes” 1997
* blog post on sex as a social construct
* The Mask You Live In, America's narrow definition of masculinity
* Introduction to Women, Gender, Sexuality Studies
* sex differences in how cold to set the air conditioner
* article on atrazine and chemical castration
* an article about South African athlete Caster Semenya and how sports struggles with the grey areas between and within, sex and gender.
* the International Association of Athletics Federations releases new rules for "female classification" based mostly on hormone levels
* Museum of Menstruation and Women's Health
* Guevedoces: girls who become boys during puberty
* article on variable expression of the SRY gene
* theories for why men have descended testicles.
* correlation between testes size and child nurturing: "Evolutionary Life History Theory posits that evolution optimizes the allocation of resources toward either mating or parenting so as to maximize fitness."
* why men have nipples
* Neurosexism: Male and female brains
* article on gay genes
* podcast with transcript on "Nature, Nurture, And Our Evolving Debates About Gender":
* podcast with transcript on sexual dimorphism, voice, and some cultural implications:
Incest is another human phenomenon that has a small basis in biology and huge cultural consequences. The biological problem with inbreeding is that it increases the chance that kids will have the same recessive deleterious alleles and be born with a recessive disease. Almost everyone has a few deleterious (bad for you) alleles, but it's not a big deal for your kids, because the chance of getting two of the same alleles is small. Because the diseases are recessive, you need to get both alleles before the disease is expressed in the phenotype, and you get the disease. But, with incest, both parents have similar DNA, and tend to have the same deleterious alleles, so the chances of their kids having recessive diseases go up.
Figure 7.12 sample of deleterious recessive and dominant genetic diseases by ???? ??????, from Wikimedia Commons (CC0)
For example, let's say Mom has Sickle Cell Trait (heterozygote, carrier, HbA-HbS) and Dad is a carrier for Tay-Sachs (heterozygote, carrier, HEXA-HEXA 4bp), the chances of their kids getting either sickle cell anemia or Tay-Sachs disease is zero. The kids might be carriers, but they won't get either disease. But, if the siblings have kids then the chances go way up.
We can calculate a coefficient of relationship to see how much genetic material you share with your relatives and a coefficient of inbreeding to calculate the increased chances of having problems, and it turns out that many cultures over-exaggerate the risks.
Figure 7.13 first cousin pregnancies from * "Will our Children by Normal?" by Christie Smith © 2000 (permission pending)
For many people around the world the advantages of having strong family ties outweigh the biological risks.
* Claus Wedekind found that potential mates who are the most genetically distant to you, and most likely to contribute to your kids' immune system, smell the sexiest.
Read an article about Trump's plan to eliminate the transgender classification from Title IX and write a letter to the editor using what you've learned about human variation.
Figure 7.14 * "Stem Cells: Egg Engineers" by David Cyranoski, Reprinted with permission from Macmillan Publishers Ltd: Nature, August 21, © copyright 2013
Why would gay men be able to have sons and daughters, but lesbian women only be able to have daughters?
All the categories of human variation in this section (age, sex, disease, race) have some basis in biology, but this last one is the most arbitrary out of all of them. The decision to group people based on superficial visual characteristics is not founded in absolute biological difference, but in a long history of cultural difference. Race is culture, not biology. We have a cultural tendency to cram human variation into racial categories.
We are stuck with lots of baggage from scientists who got it wrong. Linneaus' Systema Naturae was so definitive at the time that we still haven't been to correct his mistakes. He wrote it in Latin so it must right? In this schema Linnaeus sets up categories based on geography and cultural stereotypes, and mixes them in with biological taxonomy. This error of conflating culture and biology has been repeated for centuries, and continues to this day.
Physical anthropology is great at explaining why biological divisions between human races don't exist, but we can also suggest how we got into this mess in the first place, and why humans might be predisposed to getting it wrong. Race is an optical illusion, and our dependence on creating the world based on what we see can be explained in terms of the evolution of primates and our shift in sensory priorities from olfaction to vision. Compared to most mammals, primates see better than they smell. The visual predation hypothesis suggests how the forward-facing eyes of small carnivores predisposed them towards the binocular vision required by life in the trees. The consequences of failing to predict the correct distance of a branch can be deadly, and genes for visual acuity tend to get passed on to the next generation. Millions of years adapting to life in the trees led to primates generalized diet, including fruits. Color distinctions, especially in diurnal primates, are useful to discern whether fruit is ripe from a long distance. As we came down from the trees, the neocortex used in vision was re-purposed for increased cultural complexity such as social structure and tool use, and although encephalization has tripled the sized of our brains, we retain the vestigial primate emphasis on vision over smell. We emphasize the visually apparent differences between people because that's what our species is biologically set up to do. Dogs judge other dogs by their smell. Whales judge other whales by their songs. Bats judge other bats through echolocation. Spiders judge other spiders by their vibrations. Duck-billed platypuses judge others by their electromagnetic radiation. Trees judge other trees through mycelial networks. We look at skin color, body type, and facial features. These visual markers may seem critical to us, but they don't represent enough biological difference to separate people into significant groups.
Racism is the belief that there are discrete racial groups that can be ranked from good to bad. I had a pure-bred dog with an AKA pedigree and all, and it kind of creeped me out a little to see how seriously some of these dog breeders take their work, it reminds of the eugenics movement. Eugenics is the application of racial ideas to public policy. We blame Hitler for the most horrible atrocity in history while striving to create the master race, but many of his ideas came from the eugenics movement in the United States.
* research guide to the Black Lives Matter
* article on Mass Hysterectomies at ICE Detention Center
* article about California's role in the eugenics movement
* It was also popular in Latin America, here's an example of eugenics in Veracruz, Mexico
* Update on Racial profiling in NYPD stop and frisk policy
* Traffic enforcement in San Diego, California An analysis of SDPD vehicle stops in 2014 and 2015
* Op Ed about Census racial categories
I don't think it's possible to study race without taking sides, either for or against racism, but the study of human variation does lead to some more or less "neutral" generalizable rules about the visual characteristics we use to determine race. Most forensic anthropologists argue that they can empirically determine the race of a bone, and they get it right about 2/3 of the time.
Skim the American Anthropological Association companion site to their exhibition on RACE.
Read Dennis O'Neil on Human Variation
* Distribution of Y chromosomes among Native North Americans: A study of Athapaskan population history Question: Why does Y chromosome analysis reveal a greater admixture with Europeans than MtDNA analysis?
review Dennis O'Neil on Non random mating, an argument against people tending to choose mates from within their own race is the research on HLA and the immune system
Red hair is a good example of convergent evolution, people in many different regions around the world have different kinds of red hair, and our culture deals with it in radically different ways. Read Wikipedia on red hair
* Genetic diversity in Latinos enables chromosome mapping
Mammals tend to have darker skin towards the equator and lighter skin towards the poles.
READ THE WIKIPEDIA ENTRY ON GLOGER'S RULE
* read Peter Elias' research on filaggrin mutations, another protein like melanin that helps protect the skin.
Remember, the fact that we can study skin color scientifically doesn't mean that races are scientifically valid categories. Races are cultural defined, not biologically.
Humans, as primates, tend to be visually oriented, so it makes sense how we might create folk taxonomies based on colors.
* article on different genes that cause skin color
Other visual ways of categorizing humans are by body types and features, and many variations can be explained through natural selection. Allometry is the change in body shape when a population gets bigger or smaller depending on environmental condition. We've already had a great example in paleoanthropology of Homo floresiensis, the "Hobbit", a small hominin found on a small island in Indonesia. We attribute the small size to insular dwarfism, a principle seen in other island species; the limited island resources select for small body size.
* read more about allometry
Figure 7.15 Model T Ford radiator (public domain)
Figure 7.16 igluviak in Oopungnewing from Charles Francis Hall's Life with the Esquimaux, 1865 (public domain)
To understand Bergman's rule, think of the best and worst radiator design, and ways to maximize and minimize the surface area to mass ratio which allows heat to dissipate or be conserved. A car radiator is made with lots of flat fins for the air to pass through and wick the heat away. Some of the most efficient igluit are almost spherical to minimize the area that will dissipate heat. Natural selection tends to make humans and other mammals that way too. If you live in a hot place and need to dissipate heat, you tend to have more surface area and less mass; you're gracile. If you live in a cold place and need to conserve heat, you tend to have more mass and less surface area; you're robust. This is the best explanation for the robusticity of Neandertals: they evolved during the ice ages. The principle also explains some differences between modern regional populations.
The radiator analogy works for Allen's rule too, the longer the appendages the better they work to release heat, and the shorter the appendages, the more heat is conserved. So people who live in cold climates for long periods of time, tend to have shorter arms and legs than people who live in hot climates.
These rules apply to most animals. Bears are a great example: compare the long-legged tropical Sun Bear to the short-legged Polar bear. Human populations tend to follow this, for example the arctic Inuit tend to be stocky with short arms and legs compared to the Woodabe of sub-Saharan Africa who tend to be tall and thin. But there are some counterexamples as well, the Aka live fairly close to the Woodabe, but they tend to be short. This counterexample is probably best explained as part of the amazing human diversity on the African continent, where human evolution has occurred for the longest.
Now that we've almost finished introducing physical anthropology, it is a good time to remember how small the effect of our biology is on who we are. Yes, I'm telling you that everything you've learned up to now about the biological origins of humanity is mostly insignificant. Most research into human behavior finds biology as an almost insignificant causal factor compared to culture. We didn't evolve to be who we are, as much as we learned to be who we are. Most of who we are is determined by how we grow up: what language we speak, our religion, our favorite flavor of ice cream, our views on existentialism, what we laugh about, what we cry about.
We can accept that we are both: that biology got us most of way in the past, but by now culture has mostly taken over. The holistic approach of anthropology lets us avoid extreme views of cultural determinism or biological determinism, and we can hold seemingly contradictory views, such as bio-cultural evolution. Anthropology's skepticism of unicausal explanations makes it reluctant to force a broad unifying theory on situations where there are too many counterexamples.
Biologically analogies of culture are often misused. Recapitulation theory ("ontogeny recapitulates phylogeny") notices that human fetuses have proto gill slits, but that doesn't make us fish, and the analogy breaks down even more when applied neurology or art criticism. Social Darwinism says that poor people deserve to die because they're not fit for society, and Darwin never said or implied this. The theory of Mimetics claims that internet memes follow the same principals of Natural Selection that genes do, but they don't. They don't reproduce in the same way, they don't have introns and exons, and the way they change is more like what Lamarck described than Darwin. Have you ever heard that expression that people use to talk about how much they like a certain sports team that “it's part of our DNA”? I'd like to say that people who use that phrase are genetically stupid, but the research fails to show causation between genetics and IQ at this level. It's not in their DNA. It's in their brain. They learned it. These are examples of a general tendency to abuse biological principles and try to apply them metaphorically to cultural situations, and a kind of logical fallacy often known as a weak analogy; trying to compare apples and oranges.
As we have seen in previous sections on human variation, culture is more important than biology. Whether you get an infectious disease depends mostly on your access to clean water. Your 23rd chromosomes do NOT determine your gender; it's about your clothes, and what pronouns you use. Biological human races do NOT exist, but many cultures reify them as folk taxonomies.
Most anthropology programs separate physical (biological) anthropology from cultural anthropology because the methods and the data tend to be different, but the goal is the same. The holistic approach of anthropology is good at balancing these multiple causal factors of nature versus nurture, biology versus culture. Other branches of science do this as well, such as in behavioral ecology.
Go back and review the epigenetics section.
* Read a good review: "Culture Is Essential" the first chapter of Not By Genes Alone: How Culture Transformed Human Evolution, by Peter J. Richerson and Robert Boyd, 2005.
How much money your family has effects you biologically. Your DNA directs your cells to produce proteins to maintain normal functions, but if you lack the energy and building blocks to produce the proteins, there is no way to reach your genetic potential. The human body has an amazing plasticity to survive starvation, and this is a testament to evolutionary forces acting on our ancestors. The most significant stressors on the human body have to do with class: malnutrition, lack of clean water, exposure to harsh weather, exposure to pollution.
* stress can permanently effect your DNA
* cesarean delivery may provoke methylation that changes the genetics of a baby
The intersection between biological and cultural identities can a cumulative effect.
* Traumatic stress changes brains of boys, girls differently
Figure 7.17 "What would it be and where would it if the thing we call 'the Arts' had a biological function" copied by Arnie Schoenberg from Lynda Barry's 2014 Syllabus page 15 © 2018
Much of what we think is beautiful is determined by genetic factors that can be explained through natural selection and our evolution. The kawaii (cuteness) of manga and anime that elicits that sigh of "ahhh", happens because of our nurturing instinct towards neoteny, the retention of juvenile characteristics.
Figure 7.18 Secrets of Human Evolution Hisao Baba and Yukichi Nakao. Tankobon Book, Gakken New Manga , Secrets Series © 2008 (permission pending)
The presence of trees in beautiful landscapes, both in paintings and gardens, happens because the arboreal past that we share with primates triggers some set of neurons that were determined by genes to makes us feel good.
These pathways from gene to neuron to behavior are very difficult to trace, and this makes for exciting research in the years to come.
* Denis Dutton article on Evolutionary Aesthetics
* Creativity in Human Evolution and Prehistory, an edited book with several good articles
* Evolutionary Approaches to Creativity
* Sexy Handaxes
* Podcast on Lascaux Caves:
Music is a good example of a complex response to the nature vs nurture question. What kind of music you like is determined by the culture you grow up with. The fact that every culture around the world has music suggests that humans are biologically determined to be musical. Review the buttress drumming from primate ethology section.
* an overview of singing and human evolution.
Figures ___ Prosthetic limb by Aleksej Gerlinski, Autodesk_Online_Gallery (CC BY-NC-SA 3.0)
Popular culture thinks of cyborgs as the extreme half-robot, half-human, but thinking about human dependence on culture to augment their physical bodies, we can see that the human cyborg is not science fiction, but part of a continuum that spans our primate tool-using ancestors to the amazing interfaces of today. Human evolution, cultural progression, and the history of technology can be thought of not as some line we've crossed between "natural" and "machine" but just a question of degree, how sophisticated are the tools.
Humans use their bodies to modify the natural world, as we saw in the art of the Paleolithic revolution, but humans also use the natural world to modify their bodies. The Bafia of Cameroon believe that without scarification they are no better than monkeys or pigs (Pitt-River's Museum, Body Art). Modification sets us apart from other animals.
* Brain machine interface
* Donna J. Haraway Simians, Cyborgs, and Women: The Reinvention of Nature 1989
Homo sapiens have transformed Earth to meet their culture needs. Since prehistoric times, our subsistence practices have changed ecosystems on a planetary scale: industrialism, deforestation, agriculture, domestication.
* 33,000 years of Man's best friend in southern East Asia
previous section: 6 paleontology
next section: 8 the future
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